The co-existence of outdoor macrocellular wireless systems (e.g., cellular and personal communication systems) and indoor microcellular systems requires the prevention of mutual interference. This is easily achievable with the conventional Fixed Channel Assignment (FCA) where only a part of the whole spectrum is assigned to each of the outdoor cells.
An indoor mobile environment popping up within a cell or at the boundaries common to two or more cells has plenty of spectrum for utilization without mutual interference with the outdoor mobile conversations. With proper settings of power levels and the choice of frequencies for indoor cells the two systems can be set for interference free operation .
Dynamic Channel Assignment (DCA) has been shown to be a promising technique in enhancing the spectral utilization in the wireless communication systems. For example, see the articles by Chih-Lin I. and P. Chao, "Local Packing-Distributed Dynamic Channel Allocation at Cellular Base Station," Proc. GLOBCOM 1993 and "Local Packing-Distributed Dynamic Channel Allocation with Cosite Adjacent Channel Constraints," Proc. IEEE PIMRC 1994 and the article by M. Haleem, K. Cheung, and J. Chuang, "Aggressive Fuzzy Distributed Dynamic Channel Assignment for PCS," Proc. ICUPC 95, pp. 76. These DCA algorithms range from simple selection of a feasible channel, to maximal packing where a call request is rejected only when there is no feasible channel with all possible rearrangements. Even the simplest of them were shown to achieve very high throughput performance compared to FCA, while maintaining the link quality given by FCA. With conventional DCAs, every base station is allowed to carry out conversation with the user on any channel in the operated frequency range. Hence at a given location in the cellular radio environment, one can expect to experience interference over any part of the frequency spectrum allocated for the mobile radio operation. As such, the coordination required to avoid mutual interference between short range wireless applications (indoor) and outdoor mobile application while maintaining the capabilities of conventional DCAs is a challenging one.